Drilling fluids used in the drilling of subterranean oil and gas wells along with other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply “muds”. The functions of a drilling fluid include, but are not necessarily limited to, cooling and lubricating the bit, lubricating the drill pipe and other downhole equipment, carrying the cuttings and other materials from the hole to the surface, and exerting a hydrostatic pressure against the borehole wall to prevent the flow of fluids from the surrounding formation into the borehole.
Drilling fluids are typically classified according to their base fluid. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water which is the continuous phase. Brine-based drilling fluids, of course are a water-based mud (WBM) in which the aqueous component is brine. Oil-based muds (OBM) are the opposite or inverse. Solid particles are suspended in oil, and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds can be either all-oil based or water-in-oil macroemulsions, which are also called invert emulsions. In oil-based mud, the oil may consist of any oil that may include, but is not limited to, diesel, mineral oil, esters, or alpha-olefins.
Drilling muds must lubricate both the bearing and cutting surfaces of the drill bit as well as the string of drill pipe both upon rotation and movement along the wellbore horizontally, vertically or any angle. Frequently, in the drilling of wells and especially in directional drilling, the friction between the string of drill pipe and the sides of the borehole may be sufficient to interfere with vertical movement of the pipe into and out of the hole. Such high friction between the drill pipe and the bore hole increases power required to rotate the drill pipe and the increased torque causes wear and stress on the pipe thus decreasing the drilling rate and causing the possibility of pipe twist-off or breakage.
The lubrication characteristics of drilling fluids have been the subject of many investigations. Prior art patents disclose many types of additives for use in petroleum oil based drilling fluids, water-in-oil emulsion drilling fluids, and water-based drilling fluids. Also it has been proposed to incorporate an emulsifier in water-based drilling fluids where the lubricating additive is insoluble in water. Many of the prior additives function as extreme pressure lubricants and are added to the drilling fluid primarily to lubricate the bearings of the drill bit. Some of the known prior art additives also serve to impart sufficient lubricity to the drilling fluid to decrease the friction occurring between the drill string and the sides of the borehole thus increasing the lubricity of the drilling fluid.
It would be desirable if compositions and methods could be devised to aid and improve the lubricity of water-based drilling fluids as alternatives to those presently available to broaden the number of solutions from which the fluid designer may select.